The proposed studies will examine the neurobiological basis of cognitive functions from a comparative perspective. Both structural and functional differences in brain organization will be investigated in relation to various cognitive functions in primates. The focus of this application is on the emergence of hemispheric specialization in relation to the evolution of overall brain organization and cognitive functions from a comparative primate perspective Specifically, in addition to global changes in size and neocortical organization, the brain has become increasingly lateralized in both function and structure in primate evolution. One aim of the proposed studies is comparatively to examine global brain organization and lateralization relation to cognitive in monkeys and chimpanzees. Neuroanatomic and cognitive data will be collected in the same subjects and will therefore will resolve the existing problem of mixing data sets from different investigators. A second aim of this study is to derive measures of functional asymmetry in monkeys and chimpanzees for specific cognitive functions and to map these performance asymmetries onto structural features of asymmetry. A third aim of this research is to determine localized and lateralized cognitive functions in monkeys and chimpanzees using rapid-sequence transcranial magnetic stimulation (rTMS). In addition, individual and species variation in lateralized cognitive functions using rTMS will be correlated with area differences in corpus callosum morphology and neuroanatomical asymmetry. In part, this determination will be made by disrupting attention, executive functioning, or symbolic processing by stimulating specific regions of the cortex in monkeys and chimpanzees. Of particular interest will be the determination of whether langauge-trained chimpanzees have the functional equivalent of Broca's and Wernicke's areas. These studies will elucidate distal mechanisms involved in the evolution of human cognition including language and will provide for a better understanding of neural mechanisms involved in higher-order cognitive functions.